We statement the monitoring of porous silicon (pSi) degradation in aqueous
We statement the monitoring of porous silicon (pSi) degradation in aqueous solutions using a consumer-grade digital camera. a hypsochromic shift in the wavelength of the rugate reflectance peak resulted in visible color changes from Tenofovir Disoproxil Fumarate pontent inhibitor reddish to green. While the coordinate in the hue, saturation, and value (HSV) color space calculated using the as-acquired photographs was a good monitor of degradation at short times (parameter value calculated from the average red-green-blue (RGB) values of each image by 1st independently normalizing each channel (parameter gave consistent relative stabilities of the samples as fpSi? ?pSi-ch. coordinate [9,10]. These authors note that the coordinate is simple to calculate, is definitely easily acquired from commercial imaging products, and shows little dependence on variations in color intensity or variations in brightness of illumination. The reflectance spectra of the thermochromic liquid crystals used in thermography are similar to those of rugate porous silicon, having narrow reflectance peaks with width 30 to 40?nm [11,12]. These reflectance peaks can move over 100?nm to the blue while temperature raises. Thermochromic liquid crystal thermography often relies on a monotonic relationship between hue and temp. However, a number of authors have mentioned that the measured hue is dependent on the illuminant used and is also impacted by background reflectance [11-13]. This can result, for example, in hue not becoming monotonic if a red-rich light such as a tungsten lamp is used. Anderson and Baughn mentioned that approaches such as subtracting the amount of light in each of the reddish, green, and blue channels observed at low temp from all subsequent measurements and then calculating hue using these corrected values could give a monotonic function for all the light sources they used [11,12]. They mentioned that a monotonic function was also Tenofovir Disoproxil Fumarate pontent inhibitor acquired if they modified the white balance of their measurements using the image data corresponding to the low-temperature liquid crystal rather than images of a true gray . The concept of deriving a hue-based function after modification of the raw intensity data has been extended further. Thus, Finlayson and Schaefer applied logarithmic preprocessing to obtain Tenofovir Disoproxil Fumarate pontent inhibitor a hue parameter that was invariant to brightness and gamma , while van der Laak et al calculated absorbance for transmitted light microscopy images prior to determining a hue parameter . There are additional complexities with analyzing digital images of rugate porous silicon compared to thermochromic liquid crystals because the reflectance peaks can be narrower (10 to 30?nm) and the reflectance peak intensities can change to a larger extent with wavelength, due to factors such as light absorption within the porous silicon layer or degradation of the porous layer. In this work, we aimed to use a consumer-grade digital camera to monitor the degradation of freshly etched and modified pSi photonic crystals (rugate filters) rather than using a spectrophotometer. While this constrains the reflectance measurements to lie within the visible spectrum, measurement of the spectral changes of pSi by digital photography can enable monitoring of pSi degradation and drug delivery in non-laboratory settings. The use of digital photography for monitoring the degradation of pSi in aqueous media was validated by simultaneous spectrophotometric measurements of the pSi reflectance spectrum. Methods Preparation of freshly etched porous silicon chips (fpSi) Porous silicon was prepared by anodic electrochemical etching of highly doped 0.95 m cm p++-type (100)-oriented silicon wafers (Virginia Semiconductor, Fredericksburg, VA, USA) in a 3:1 (aqueous acetic acid and stirring overnight. The fpSi sample was coated with chitosan by spin coating (Laurell WS-400B-6NPP-Lite, Laurell Technologies, North Wales, PA, USA) using 150?L of chitosan solution at a final speed of 100?rpm for 10?min and then drying at room temperature under nitrogen. The sample was then placed under vacuum to evaporate the remaining solvent. After the deposition, the pSi-ch samples were heated at 70C on a hot plate for 10?min to cause a small amount of polymer infiltration into the pores, and this resulted in Tenofovir Disoproxil Fumarate pontent inhibitor a slight red shift in the rugate reflectance peak position. Instrumental procedures The porosity and thickness of the porous silicon layers were estimated by the spectroscopic liquid infiltration method (SLIM), based on the measurement of the thin-film interference components of the reflectance spectra of the samples before and after infiltration of a liquid (ethanol) with known refractive index  by using an Ocean Optics USB-2000 spectrometer (Ocean Optics, Dunedin, FL, USA) configured for specular reflectance, working in back-reflection configuration in the range 400 to 1 1,000?nm. The reflectance spectra were recorded at five spots distributed across each sample in order to evaluate the homogeneity of each porous silicon sample. The values of the porosity and the thickness had been determined by method of the two-component Bruggeman effective moderate Rabbit Polyclonal to Synuclein-alpha approximation . The degree of chitosan infiltration in to the porous silicon sample was also evaluated from the reflectance spectrum. The freshly ready (fpSi) and altered (pSi-ch) porous silicon samples had been characterized utilizing a Thermo Scientific.